1. Technical Field of the Invention
The present invention relates to an apparatus for rectification of liquid mixtures and/or for scrubbing of gases.
2. Prior Art
Apparatuses for rectification of liquid mixtures and apparatuses for scrubbing of gases function in principle in the same way, namely by causing the atomised liquid and the gas phase to flow counter-currently and thus to come into mutual contact. The reason why apparatuses for rectification and apparatuses for gas scrubbing have usually been built differently is that the reaction between the gas and the liquid phases is different in the two kinds of apparatuses. In rectification heat and substance is transferred between liquid and vapour when the heat transmission coefficient is high. For high viscosity mixtures, however, a high atomising velocity is necessary. In gas scrubbing the washing liquid in an atomised condition and the gas to be purified are caused to flow counter-currently at a high velocity. It has been found, however, that the solid particles entrained by the gas may avoid to come into contact with liquid and to be removed from the gas when the velocity of the liquid droplets is relatively low. In gas scrubbing centrifugal pumps are usually used for atomising liquid which is re-circulated. Because it is rather complicated to use a plurality of scrubber stages, usually only a single stage is used, and then the gas being discharged from the scrubber has only been in contact with a relatively dirty liquid, which has not been utilised at an optimum.
WO 97/18023 comprises an apparatus including a rotative heat transmission body for evaporating liquids or drying pumpable products. The apparatus comprises a scraper for continuously scraping solid deposits from the evaporation surface of the rotating heat transmission body. It has been found that when such a rotative heat transmission body is used for treating a mixture of liquid having different boiling points and a rotating atomising device is used for throwing droplets on to the evaporation surface of the heat transmission body, a rotating movement is also imparted to the vapour generated. Consequently, an exact counter-current movement between the two phases can not be obtained, and this is necessary to obtain an efficient rectification or scrubbing.
WO 91/01784 discloses an apparatus for rectification and gas scrubbing. Liquid is repeatedly thrown through the gaseous phase against an inner peripheral heat transmission surface. Spraying or atomising the liquid by means of a rotor causes a pressure reduction where the liquid droplets leave the rotor and a corresponding pressure increase where the droplets are stopped. The pressure difference so created may partly be equalised by transverse gas flows at the end walls of the processing chamber and by a resulting axial flow within the apparatus impairing the efficiency of the apparatus.
The pumping effect caused by the liquid droplets being thrown radially outwardly by the atomising rotor is volumetrically far greater than the volume of the vapour flowing through the apparatus. The adverse result is that liquid droplets being thrown radially outwardly adjacent to an outlet for remanence come into contact with vapour having a relatively high content of the volatile component, and due to the equilibrium between the two phases the remanence will have a higher content of the volatile component than necessary. It is true that the evaporated vapour being exhausted through a vapour outlet at the other end of the apparatus adjacent to the inlet of the raw product to be processed has a high content of the volatile component. However, when it is mixed with re-circulated vapour the concentration of the volatile component of the distillate is reduced.